QPromise: run continuation(s) on destruction

If the QFuture is canceled because the associated QPromise has been
destroyed, we still need to run its continuations (i.e. onCanceled
handler, if it's attached), so replaced the cleanContinuation() call
inside ~QPromise() with runContinuation(), which will also take care of
cleaning the continuation.

[ChangeLog][QtCore][Important Behavior Changes] QFuture now runs its
continuations when its associated QPromise has been destroyed.
Previously, if a QFuture was canceled because the associated QPromise
has been destroyed, its continuations were skipped.

Fixes: QTBUG-103992
Pick-to: 6.4 6.3 6.2
Change-Id: Ie05bc760c96c349aade8adb8d2fe5263aff8efac
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

1 files changed, 20 insertions, 0 deletions

diff --git a/tests/auto/corelib/thread/qpromise/tst_qpromise.cpp b/tests/auto/corelib/thread/qpromise/tst_qpromise.cpp
index 5de8ce13ab..12206aa9fc 100644
--- a/tests/auto/corelib/thread/qpromise/tst_qpromise.cpp
+++ b/tests/auto/corelib/thread/qpromise/tst_qpromise.cpp
@@ -40,6 +40,7 @@ private slots:
 #endif
     void cancelWhenReassigned();
     void cancelWhenDestroyedWithoutStarting();
+    void cancelWhenDestroyedRunsContinuations();
     void finishWhenSwapped();
     void cancelWhenMoved();
     void waitUntilResumed();
@@ -494,6 +495,25 @@ void tst_QPromise::cancelWhenDestroyedWithoutStarting()
     QVERIFY(future.isFinished());
 }
 
+void tst_QPromise::cancelWhenDestroyedRunsContinuations()
+{
+    QFuture<void> future;
+    bool onCanceledCalled = false;
+    bool thenCalled = false;
+    {
+        QPromise<void> promise;
+        future = promise.future();
+        future.then([&] {
+            thenCalled = true;
+        }).onCanceled([&] {
+            onCanceledCalled = true;
+        });
+    }
+    QVERIFY(future.isFinished());
+    QVERIFY(!thenCalled);
+    QVERIFY(onCanceledCalled);
+}
+
 void tst_QPromise::finishWhenSwapped()
 {
 #if !QT_CONFIG(cxx11_future)